The ITU Telecommunication Standardization Sector (ITU-T) has issued a Recommendation of an optical transport network (OTN) as a platform of transparent transport. The transparent transport allows client signals to be communicated between end users without any concerns of higher layers and lower layers of not only synchronous networks such as a synchronous optical network (SONET) or a synchronous digital hierarchy (SDH) but also asynchronous networks such as Internet Protocol (IP) or Ethernet (Registered Trademark) in the wavelength division multiplex (WDM) system that is adapted for explosive growth of the Internet traffic. The OTN is rapidly introduced into commercial systems as interfaces and formats for the OTN are already standardized based on Recommendation G.709 issued by the ITU-T. Henceforth, a method for constructing an optical network may play an important role for flexibly operating OTN signal paths utilizing an OTN cross-connect (XC) device.
Initially, a process of accommodating demands into an optical path is described with reference to FIGS. 1A and 1B. Note that an optical channel data unit (ODU) frame serving as a lower-rate signal transport frame that accommodates client signals is called a “lower order ODU (LO-ODU)”, and an ODU frame that multiplexes and accommodates such low-rate ODU frames is called a “higher order ODU (HO-ODU)”. In the OTN, the HO-ODU serving as an optical path accommodates the LO-ODU accommodating client signals by issuing a demand for specifying a signal transmission route from a start-point node to an end-point node.
For example, in FIG. 1A, a demand D1 specifies an optical path having a route of nodes 1, 2 and 3 (a start-point node is node 1 and an end-point node is node 3). A demand D2 specifies an optical path having a route of nodes 4, 3, 5 and 6.
The optical paths are implemented by the HO-ODU. For example, in FIG. 1B, the optical path P1 of the HO-ODU is configured between the nodes 4 and 3 and between the nodes 3 and 5. Further, the optical path P2 is configured between the nodes 5 and 6. The aforementioned demand D2 that specifies the optical path having the route of nodes 4, 3, 5 and 6 is implemented by the optical paths P1 and P2.
Meanwhile, there are proposed technologies for suppressing the increase of computational time in designing of the optical path (e.g., Patent Documents 1 and 2). These technologies introduces the concept of the “constraint of solution space” in the designing of the optical path within the optical network by mathematical programming in order to suppress the increase of computing time.
Further, there is proposed a minimization design for minimizing cost of links and nodes corresponding to the probabilistic demand pattern (e.g., Patent Document 3).